create 64 small controllers with a driver circuit for the motor (H bridge ) and a minimal Arduino . Hook them all up on a RS485 bus. Have a central master that controls all the small controllers.
A bit more info about the project would maybe help. You say to raise/lower 64 objects of about 5KG weight by about 25mm but will the movement be either fully up/down or can it be any position between. Also how fast must it raise/lower.
If you're using stepper motors to control an absolute position, you will need some way to find/set the initial reference position. Maybe just parking the motor against a mechanical stop or limit switch?
Each ATtiny85 is programmed with its own unique 6-bit address number (0-63), and listens for 2-byte instructions over a common serial interface from the central Arduino. The first byte of info is the address, the following byte is a command to turn x number of revolutions in y direction, which the selected ATtiny85 translates into instructions for the ULN2003 board using the "stepper_oneRevolution" code.